1. Field of the Invention
This invention relates to a digital signal recording methods to be used suitably for high density recording of digital signals of digital video tape recorder (VCR) or the like.
2. Description of the Prior Art
Conventionally commercially available digital VCRs (hereinafter abbreviated as DVCRs) are exclusively used for broadcasting purposes, in which the recording is, performed in the block form as shown in FIG. 2. That is, the recording block consists of a synchronous pattern showing the top block thereof, an ID showing the information of a recording data and the recording data. When reproducing, the synchronous pattern is detected to identify the top block thereof, and then, the ID or data are restored.
With the conventionally commercially available DVCRs for broadcasting use, the synchronous pattern for the video data and that for the audio data are identical. The audio data and video date are added as a part of the ID block in FIG. 2 with respective special identification codes mutually identifiable for each recording block in which the data are contained and then, recorded. On the other hand, when the reproduction is to be carried out, the reproducing data is identified if it is video or audio in response to the identification code thus added thereby switching the following processings in accordance with the result therefrom.
As shown above, with the DVCR, when reproducing, the video and audio data have different processings depending on the identification codes in respective recording blocks. As a result, if the identification code is erroneous, such a case may happen in which the video data is processed as audio data and vice versa. It typically exemplifies the fact that an extremely small error results in an extremely large error, arising in a critical problem on a practical basis.
Since the conventionally commercially available DVCRs are for broadcasting use, a lot of circuit means are provided in order to prevent errors in the identification code, thereby overcoming such a problem as shown above. In this case, however, referring to DVCRs for the home use which will be commercially available in the future, large-scale circuit means cannot be packaged on a cost effective basis as a measure to prevent errors in the identification code as DVCRs for broadcasting use. Accordingly, to find a method which is comparatively easily capable of largely reducing the error generation in the identification code is a critical theme for realization of home-use DVCRs.
On the other hand, at present, in the magnetic recording field, the development of narrow tracking technology is in progress in order to improve the recording density: For example, with home-use VCRs now on sale, signals are recorded obliquely on a tape as shown in FIG. 9. The locus thus formed on the tape is called a track, the effective width of which being called a track pitch (TP).
At present, the track pitch is less than 30 .mu.m, and it is not an impediment if the track is handled substantially linearly due to the fact that the track may be curved resulting from a lack of accuracy in the mechanical system and a reduced amount of the actual track pitch ranges from 2 to 3 .mu.m. This means that the effect of the track curvature can be ignored.
However, in case of setting the track pitch to be less than 10 .mu.m, for example, to be 5 .mu.m in order to improve the recording density, a problem such as that shown in FIG. 10 will arise. Namely, a track curvature as mentioned above narrows the effective track width up to about half of the actual widths. A reduction of the track pitch causes the signal power to be lowered and the reliability of the signal to be decreased, so that when the effective track width is only half of the actual track pitch, the reliability of the signal will be significantly decreased.
For the reasons as shown above, in case of narrow track recording, a function to control the height of a head so as to follow the head to the track curvature is additionally provided. This function extracts a special frequency (hereinafter called a pilot frequency) for tracking which is recorded on the track superposed on the signal from the reproducing signal by providing the head to the top end of a piezoelectric element and controls the voltage to be applied to the piezoelectric element in response to the level of the pilot signal thus extracted. As a result, the head can accurately trace the track curvature, so that the effective track width can be substantially equal to the actual track pitch.
However, in case of superposing a pilot signal on a signal, it is conventionally recorded in an analog fashion so as to be superposed upon the signal. In this case, the pilot signal is equivalent to noise from the stand point of the signal. As a result, if the recording level of the pilot signal is made excessively large in order to make sure of accurately extracting the pilot signal, a lot of noise is recorded so as to be superposed upon the signal, resulting in an increase in error.
On the other hand, if the recording level thereof is excessively small, the pilot signal cannot be extracted correctly. In addition, even if a suitable recording level of the pilot signal exists, it will be varied depending on the VCR deck to be used for recording. Accordingly, there arises a problem in that the deck must unavoidably require a lot of time for adjustment during the manufacturing thereof.